Muffler



Jan- 23, J MaCKENZEE ET AL Jan. 23, 1940. R., J. MacKENzIE ET AL MUFFLER2 Sheets-Sheet 2 Filed May 3, 1934 mmm/FJ Q/ Patented Jan. 23, 1940UNITED STATES PATENT OFFICE MUFFLER pany, Buffalo, N. Y.

Application May 3, 1934, Serial No. 723,735

15 Claims.

` This invention relates to improvements in mufflers or silencers of thetype intended to silence the noise accompanying a stream of gases, as,

- for example, happens in connection with the exhaust of an internalcombustion engine.

The objects of this invention are to provide an improved structure ofthis kind having an inner passage or shell for the gases which isprovided along the greater portion of its length With Va large number ofrelatively small apertures, and having sound deadening chambers ofimproved construction arranged about said inner shell; also to provide amuffler having a plurality of spaces,

each successively communicating with another to receive sound Waves andgases, and having means to cause gases to move in different directionsin different chambers, and to pass from one chamber to another in adirection substantially at right angles to the direction of movement ofthe gases in the other Chamber; also to provide an improved method ofmuflling sound by means of which sound waves travel to and from bodiesof gases in a direction substantially at right angles to the directionof motion imparted to the gas as it moves through the perforations inthe inner shell into the chambers occupied by these bodies o-f gas; alsoto provide an inner shell of this kind and having portions of the innershell projecting outwardly at or near said apertures, and also havingone or more outwardly extending annular ridges or projections to whichbafi'les or the like may be secured between series of said apertures;also to provide a muier of this kind in which two or more chambers areprovided which are connected by means of one or more sound- 'conductingchannel or neck portions; also to provide a mufiler of this kindprovided with an inner shell through which the gases fiow lengthwise,

and a plurality of chambers formed about the 40 inner shell in which thegases fiow in a substantially circumferential or tangential directionrelatively to the inner shell; also to provide a muiller of this kind inwhich some of the chambers having a substantially circumferential motionare connected with resonator chambers; also to improve the constructionof mufflers of this type in other respects hereinafter specied.

In the accompanying drawings:

Flg. 1 is a longitudinal central sectional view of a mufiler embodyingthis invention.

Figs. 2 and 3 are transverse sectional elevations thereof onlines 2-2and 3-3, respectively, of Fig. 1.

Fig. 4 is a longitudinal central sectional view of a mufller of modifiedconstruction.

Flg. 5 is a transverse sectional elevation thereof on line 5 5, Fig. 4.

Fig. 6 is a longitudinal central sectional elevation of a portion of amufiler of still another modified construction, and Fig. 6a is theremaining portion or continuation of the same muifler.

F'ig. 7 is a transverse sectional elevation thereof on line 1-1, Fig.6a.

Fig. 8 is a fragmentary longitudinal central sectional elevation of theend portion of a mufller of modified construction.

Fig. 9 is a transverse sectional elevation thereof on line 9-9, Fig. 8.

Fig. 10 is a fragmentary longitudinal central sectional view thereof online lll-|ll, Fig. 9.

In all of the several constructions shown, We have provided asubstantially continuous straight through passage for gases and soundWaves and about this passage are arranged a series of chambers into someof which gases pass through perforations or apertures in the passage,and in such chambers means are provided for imparting movement to thegases, such for example as a whirling movement on a motion substantiallytangential to the circumference of the perforated shell. Other orsecondary chambers connect with the chambers containing moving gases andreceive sound Waves and gases in a direction at an angle to thedirection at which the gases emerge from the perforated shell, and soundWaves on refiection from these secondary chambers are returned to thefirst chambers in a direction such that they encounter thecircumferential motion of the gases in these chambers at an angle andlikewise the sound Waves carried by this moving gas, thus causinginterference and modification of these sound Waves in such a manner asto decrease the intensity of the sound Waves.

Referring to Figs. 1 to 3, the mufiler includes an inner shell, tube orconduit Ill having perforations throughout the greater portion of thelength thereof, an outer imperforate shell l I, and baflies or heads [2and 13 which may form end Walls of the mufler, and which, in theparticular construction shown, extend from the outer to the inner shelland are secured to both of these shells. These baflies 01' headspreferably have tubular projections M yand IS to which pipes or tubescarrying the stream of gases may be connected. When the mufiler is usedfor silencing the exhaust of an internal combustion engine, the exhaustpipe is connected with the projection I 4 at the inlet end of themuffier and the usual tail pipe may be connected to the projection l5.The muffler also includes one or more intermediate shells, a singleintermediate Shell IS being shown in the construction illustrated inFigs. 1 to 3.

The inner shell is provided with a relatively large number ofperforations l'l extending throughout the greater portion of the lengththereof and the metal adjacent to these perforations is preferablyformed or drawn outwardly in such a manner as to form louvers or vanesl8 which serve to deflect or guide the gases passing out through the'apertures in a substantially tangential direction. A series of theselouvers arranged about a circumferential portion of the inner Shell willproduce a strobic action or tangential motion of gases in the chambersurrounding the inner shell, and the sound Waves passing out throughthese openings will be deflected in a similar manner. The louvers in theinner shell may extend all in one direction so as to cause'all of thegases between the inner and intermediateV shells to move in the samedirection, or the gases in different portions of the space between theinner and intermediate shells may be discharged in different directions.Ifdesired, the gases in a single chamber surrounding the inner shell maybe divided into two or more bodies and adjacent bodies may whirl inopposite directions, this being eifected by a corresponding arrangementof the louvers.

These perforations in the inner shell, in the form shown in thedrawings, are elongated, being several times longer than their widths,and they are arranged non-perpendicular to the general direction of fiowof gases through the inner shell. The perforations present sharpcorn'ers at the vleading and tr'ailing ends thereof and have no faceswhich are perpendicular to the flow of gases in the inner shell. Becauseof this structure, the perforations avoid the creation of whistling orhissing sounds sometimes produced by circular perforations.

It is desirable to divide the space between the inner and intermediateshells into a series of chambers, some of which may be of differentlengths than others. It is, of course, customary to divide the spacebetween two tubular shells by means of bafiies, but where projections orlouvers 18 extend outwardly from the outer surl face of the inner shell,the securing of baffies to the inner shell to form substantiallyair-tight joints therewith is not possible with such inner shells asordinarily construoted. To overcome this dificulty, we have provided theinner shell at the ,portions thereof at which the baflies are to bearranged with outwardly extending annular ridges or raised portions 20,see Figs. 1 and 3, the outer surfaces of these annular ridges extendingoutwardly beyond the cylindrical surface of the inner shell to an extentequal to or greater than the extent to which the louvers 18 extendoutwardly. Consequently, in the assembly of a mufiier, baffles 2| may bepassed lengthwise of the inner shell, thus clearing the louvers 18, andsuch baifles Will fit snugly against the annular ridges 20 and may bespot-welded or otherwise secured thereto. p

24 represents a baffie spaced between the intermediate and outer shellsto divide the space between these shells into two outer chambers. One ormore of these bafi'ies may be employed, as desired, or such bafiles maybe entirely omitted. In the construction shown in Fig. 1, this baflledivides the space between the intermediate and outer shells into twoouter chambers 25 and 28 and the space between the inner andintermediate shells is divided into inner chambers 21, 28, 29, 30 and3|.

The two-end chambers 21 and 3| are preferably connected with the outerchambers 25 and 26 respectively by means of passages in the muflierwhich are so arranged that sound can travel into the outerkchambers 25and 26 only after it has been acted upon by the inner chambers 21 and3|. or in other words, the connecting passages or Channels between thetwo inner and outer chambers are such that sound cannot pass directlyfrom the interior of the inner shell to the outer chambers. It has beenfound that very decidedly silencing effects are producecl in thismanner, and these results can, of course, be obtained by means of anumber of different constructions, those illustrated in the drawingsbeing merely examples showing how our invention may be used.

ItV is not intended to limit this invention to the constructionillustrated.

In certain cases, superior results are obtained when the passageconnecting an inner and an outer chamber is of restricted nature. Ifsuch an arrangement is desired, this can be accomplished by means of theconstruction shown in Fig. 1, in which the end portionsof theintermediate shell are'deforrned out of their cylindrical shape in sucha manner that portions 33 of the intermediate shell will lie in contactwith portions of the inner shell, see particularly Fig. 2, while otherp'ortions 34 of the ends of the intermediate shell are left in anoutwardly bowed form to form constricted sound conducting Channelsleading from the inner chambers 21 and 3| to the outer chambers-25 and25 respectively. It will be noted also that the perforations in theinner shell terminate at a distance from theends of the intermediateshell, so that a sound. conducting passage is formed in which soundWaves from the inner chambers 21 and Si may pass into the outer chamberswithout interference by the sound waves of the interior of the innershell.

It will be noted in Fig. l, that the baffie in the space between theintermediate and outer shells is located so as to form resonatingchambers of two different lengths. The locationof the baifie 24 depends,of course, to a large extent upon the particular sounds which are to bemuffled. 'The chambers 28, 29 and 38 are not in communication witheither of the outer chambers, since it has been found desirable toprovide some sound deadening chambers of this type. It is not, however,essential that only the end chambers communicate with the outerchambers, since equally good results vcan be obtained by establishing asound conducting passage between any of the intermediate chambers, andan outer chamber.

It will be noted that in the muffler described,

sound Waves and gases pass lengthwise in the inner shell, in a circularor tangential direction in the inner chambers, and lengthwise of themuifler in the outer chambers. Furthermore, sound Waves passing, forexample, from the inner chamber 21 at substantially right angles to thedirection of motion of the gases in the chamber 21, and also any soundWaves returning from the outer chamber 25 through the neck or channel34, enter the inner chamber 21 at right angles to the 'direction oftravel of gases and sound Waves inl` the chamber 21. This results in avery effective deformation of the sound Waves, so that very efiectivesilencing results.

In Figs. 4 and 5 is disclosed a slightly modified type of muffler whichdiffers from the muffler shown in Fig, 1 mainly in that the intermediateshell 35 is not bent inwardly at the ends thereof as shown in Fig. l,but is of continuous cylindrical form. In this construction, the louversIB in the inner shell terminate at a distance from the ends of theintermediate Shell so that sound` conducting passages or Channels arefornied between the inner and intermediate shells at the ends of theseshel1s,` through which channels sound and tion With F'igs. 1 to 5inclusive.

, certain sound Waves from the exhaust.

gases can pass to theouter chambers 36 and 31 between the intermediateand outer shells. At the right end of the muliler shown in Fig. 4, theend of the intermediate Shell is unsupported, and at the left end asupporting bafile 38 is provided, which preferably has apertures 39therein through which sound Waves may pass into the outer chamber 36.The operation of the muffler shown in Figs. 4 and 5 is identical withthat shown in Figs. 1 and 3, and the same tangential motion of the gasas it leaves the inner Shell and enters intermediate chambers isattained as before, and provision is made for sound Waves and gases toleave and return to these chambers in a direction approximately at rightangles to the directions of the tangential motions.

Figs. 6, 6a and 7 illustrate a muffler of the dumb-bell or sectionaltype, in which the muflier is constructed in three Sections. The firstsecfl tion is provided with an inner Shell 46, an intermediate Shell 4I, and an outer shell 42. Baflles 43, 44 and 45 divide the space betweenthe inner and intermediate shells into two sound deadening chamberssimilar to those employed in connec- One end of the intermediate shellterminates at a distance from the end of this section of the muflier,and consequently, a portion of the perforations or louvers |8 of theinner shell will discharge gases into a chamber 46 formed between theinner Shell and the outer Shell of this section of the muffler, and aresonating chamber 41 is also formed between the imperforateintermediate Shell and the outer Shell. Sound Waves and gases may travelinto and out of this resonating chamber in a direction substantiallyperpendicular tothe direction of movement of the gas in the chamber 46.

The gases discharged from the first section of the muffier enter intothe second section which includes inner, intermediate and outer shells,the space between the inner and intermediate shells being divided into aSeries of chambers 48, 49 and 56, the chambers 49 and 56 having nocommunication with the outer chamber 5| of this section of the mufller.The chamber 48, however,

` communicates with the outer chamber 5| through the open end of theinner shelland through apertures 52 formed in a baffle 53. The aperturesor louvers |8 of the inner shell terminate at a slight distance from theapertures 52 in the baffle 53 so as to form a sound-conducting passageconnecting the chambers 48 and 51 for carrying only such sound Waves tothe outer chamber 5| as have been subjected to the action of the chamber48.

The third section of the mufiler is formed to produce inner chambers 55,56 and 51 and outer chambers 58 and 59. At the discharge end of thisSection of the muffler, an enlarged chamber is provided which extendsfrom the inner Shell to the outer shell of the mufer, and whichcommunicates with the chamber 59 through holes 6| in a bafiie or head62, thus forming a sound absorbing chamber of a different Shape toeliminate In this case, gases entering the chamber 60 from the innershell are given a motion tangential to the inner Shell by passagethrough the louvers |8. Sound Waves may pass laterally from the movinggases through the apertures 6| into the resonating chamber 59, and ifany sound Waves are deflected or returned by reflecton from the baflieat the end of the chamber 59 to the body of gas in the chamber 6D, suchrefiected or returned Il Waves will strike the moving gases atsubstantially a right angle to their direction of movement, thus causinginterference and modication of these sound Waves in such a manner as todecrease the intensity of the sound Waves.

It will be noted that the outer chamber 5| of the second section of themuflier is connected with the outer chamber 58 of the third section bymeans of a relatively small tube or passage 64. A single tube of thiskind is shown connecting the two chambers, but more tubes may beemployed, if desired. This connection between the two outer chambers hasbeen found to produce results comparable to those obtained with a singlechamber of greater length than that of either of the individual chambersor with proper size of connecting tube or tubes to results obtained witha single chamber of length equal to or greater than that of the combinedlength of the two chambers. This construction is, therefore, verydesirable, particularly in cases where long mufllers are required toeliminate the sound waves from a particular engine, and where the underframes of the vehicle are so arranged that such long mufiiers cannot beemployed.

Various modified forms of sound-conducting passages, channels or necksfor transmitting sound from one chamber of the muffier to another may,of course, be employed in connection with this invention. Another suchpassage of modified form is illustrated in Figs. 8 to 10 inclusive, inwhich the intermediate Shell 61 is provided at its ends with inwardlyindented or pressed portions 68 extending into contact with the innershell 69. This arrangement provides relatively large sound conductingpassages or necks 19, and if a still longer neck is required to producethe effective silencing of certain sound Waves, a second intermediateShell or sleeve 12 may be employed which may be secured at one end tothe outer head or bafile 13 of the muiller and spaced from the innerShell by means of a Spacing member 14 and arranged in contact with theportions of the end of the intermediate shell 61, which are not indentedor pressed inwardly, as clearly shown in Fig. 9. This arrangement,consequently, forms additional sound-conducting passages or necks 15through which the sound passes in the passages 10 and enlarged spaces 16are also provided between the intermediate shell 12 and the inner Shell69, in which the direction of travel of the sound Waves and gases isreversed. In this construction, the sound Waves and gases enter into theouter resonant chamber 'l'l intermediate of the ends thereof, and thusproduce a silencing effect which is different from that re- Sulting whenthe sound is admitted into an end of the resonant chamber.

In all of the constructions described, the mufflers develop very littleback pressure, since the gases flow straight through the muifler fromend to end thereof. Since each design of internal combustion enginedevelops sound Waves in the exhaust which are different from anothertype of engine, lt will, of course, be understood that mufflers of thistype must be adjusted to suit the particular design of engine with whichthey are to be used. Consequently, the length of the muffier and thenumber of sound deadening chambers contained 'therein will varymaterially, depending upon the nature of the engine with which themuffler is to be used, and the location of the bafiles, as well as thediameters of the shells are also varied to produce the desired results.By providing the mufliers With neck portions connecting one mufllingchamber with a second, such second Chamber -With its entering neckportion provides a type of resonator which Supplies destructiveinterference for sound Waves in Certain frequency bands as they attemptto pass through the mufiier. The inner chambers arranged betweentheinner and intermediate shells are capable of eliminating veryeffectively certain sound Waves- The mufler may be so tuned thatdestructive interference of sound Waves in one vfrequency region Willresult from the action of Chamber 25 While destructive interference inanother frequency region Will result from the action of Chamber 21. Thecombination of these chambers provides means for eliminating sound Wavesor reducing their intensity over a considerable band of frequencies orin several different frequency regions. By making the chambers 3l and Eof different lengths from the chambers 25 and 27, the two chambers 3|and 26 will Cooperate with each other for the elimination of other soundWaves, than those eliminated by the Chambers-Z and 21. Furthermore, thechambers 29 and 3G being of different dimensions Will each eliminatedifferent sound. Waves, and if certain objectionable sound Wavespredominate in the exhaust and are difflcult to eliminate, two similarchambers like the chambers 28 and 29 can be employed to eliminate suchsound Waves. This description of the operation of the construction shownin Figs. 1 to 3 applies equally well to the various types of .soundreducing chambers employed in the other modified forms shown.

It will be noted that in all of the constructions illustrated, some ofthe chambers in which gas moves tangentially to the inner shell areconnected With outer resonating chambers so that gases and sound Wavespass from such a Chamber to an outer resonating Chamber, and this hasbeen foundto be very effective in silencing noises, particularly if theouter Chamber communicates with the first Chamber by means of a passageso arranged that the motion of gas and sound Waves between'the twochambers is substantially at right angles vto the tangential motion ofthe gas as it enters the first Chamber from the perforated inner shell.This method of silencing the exhaust has proven very effective and itappears that When sound Waves travel in a moving gas, destructiveinterference of the sound Waves takes place When the sound Waves passfrom a body of gas moving in one direction into a body of gas moving inanother direction.

It has also been found advantageous to alternate the direction ofrotation of the gases in different inner chambers by reversing thedirection of the vanes or louvers inthe inner shell, although thisalternate arrangement of the louvers is not essential to the successfuloperation of the mufflers.

' We Claim as our invention:

1.V A muffler having a substantially straight unobstructed passagetherethrough for gases and sound Waves, said passage having aperturestherein, a Chamber receiving gases and sound Waves from said passagethrough said apertures, meansV for defiecting gases entering into saidChamber in a direction substantially tangential With regard to saidpassage, and a. second Chamber having a reduced neck for receiving soundWaves from said first Chamber in a drection substantially perpendicularto said tangential direction, and having nov direct communication withsaid passage, said reduced neck being of smaller cross sectional areathan the cross sectional area of said first mentioned Chamber.

-2. A muffler having a shell provided throughout the greater part of thelength thereof With perforations and having outwardly extendingprojections adjacent thereto, another shell arranged about said firstmentioned shell, a transverse baffle connecting said shells, and anannular out- Wardly extending ridge on said first shell, the outer partof which extends'outwardly at least as far as said projections and towhich said baffle is secured, Wher-eby said baffie may be passedlengthwse of said first mentioned shell over the projections thereoninto engagement with said ridge.

3. A mufiier having a shell provided throughout the greater part of thelength thereof With a piurality of groups of perforations having out-Wardly projeC-ting portions adjacent thereto, said shell having anannular unperforated portion, an outwardly projecting ridge on saidannular unperforated portion, the outer portion of said ridge exten-dingoutwardly at least so far asisaid projections, and an annular transversebafile having an internal diameter greater than the external diameter ofsaid shell measured to the peaks of said projections, said baflle beingsecured to and forming a close fitting connection withl said ridge.

4. A mufler having a shell provided throughout the greater part of thelength thereof with a piurality of groups' of perforations having out-Wardly projecting portions 'adja-Cent thereto, said shell having anannular unperforated portion provided With an outWar-dly pressed annularridge formed in said shell, the outer surface of said ridgc extendingoutwardly at least so far as said projections, and a transverse bafilesecured `to said outvvardly extending ridge.

5. A mufiier having an inner shell provided with a plurality ofrelatively small perforations, an outer imperforate shell having itsends closed, an intermediate shell, said inner and intermediate shellsforming between them an inner Chamber and said intermediate and outershells forming between them van outer chamber,` means Cooperating Withsaid iperforations for deflecting gases discharged through saidperforations in substantially tangential directions relatively to saidinner shell, and a sound conducting passage of smaller Cross sectionalarea than either of said chambers and connecting said inner and outerchambers and arranged in such angular relation to said tangentialdirections as to prevent the straight passage of sound Waves from saidpassage to said perforations.

6. A mufiler having an inner shell provided With a plurality ofrelatively small perforations arranged to discharge gases substantiallytangentially of said inner shell, an outer imperforate shell having itsends closed, an intermediate shell, said inner and intermediate shellsforming betWeen them an inner Chamber and said intermediate and outershells forming between them an outer Chamber, said inner Chamberreeeiving gases and sound Waves from said inner shell through saidperforations, and a passa'ge Connecting said inner and outer chambersand of greater length than width in a radial direction and of less crosssectional area than said inner Chamber and extending lengthwise of saidmufller' on Said inner Shell for directing gases and sound Waves intosaid inner chamber in a dlrectio i f gential to said inner Shell, and aneck co' Said inner chamber :id said outer chamoer which extendssubstantially lengthwise of said muffler and which is of smaller crosssectional than either of said chambers.

8. A muffler provided With a plurality of Shells for provlding asubstantially Straight inner pas- Sage for gases and inner and outerchambers surrounding Said passage, said p'assage being provided withperforations through which gases and sound Waves may pass from saidpassage to an inner chamber, means for discharging Sound waves in asubstantially tangential direction into said inner chamber, and a secondpassage leading from said inner chamber to said outer chamber andextending substantially in a direction parallel to the axis of saidinner chamber and of Smaller cross section than said inner Chamber.

9. A mufller having an inner Shell provided with a plurality ofrelatively Small perforations, an outer imperforate Shell, bafilesconnecting Said inner and outer shells, an intermediate Shell arrangedbetween said inner and outer shells and between said balfles, an end ofsaid intermediate Shell having a portion pressed nwardly toward Saidinner Shell to form a restricted passage for gases between said innerand intermediate shells, and a sleeve extending from a baifle over apart of said inwardly pressed portion of said intermediate Shell to formbetween said sleeve and Said inwardly pressed portion of saidintermediate Shell a return passage for gases.

10. A muflier including an inner perforate Shell forming a passage forgases and Sound Waves through the muffler, an intermediate Shellarranged about said inner Shell and terminating short of the endsthereof, an outer Shell arranged about Said intermediate Shell, headsclosing the ends of said outer Shell and provided with openings throughwhich gases may pass to Said inner Shell, Said inner Shell havingimperforate portions arranged adjacent to the ends of Said intermediateShell, a baffle dividing the space between said intermediate and outerShells into resonance chambers, the ends of Said intermediate Shellabout Said imperforate portions of Said inner Shell being provided withinwardly pressed grooves, the inner Surfaces of which are secured toSaid imperforate portions Of said inner Shell, said grooves beingarranged between portions of said ends of said intermediate Shell whichare Spaced from said imperforate portions of Said inner Shell to formchannels leading to Said resonance chambers, said channels being incommunication with perforated portions of Sai-d inner Shell to receiveSound Waves therefrom and conduct the same to Said resonance chambers.

11. A muliier including an inner Shell through which gases and soundWaves pass, an outer Shell and an intermediate Shell extending aboutsaid inner Shell, transversely extending members arranged between saidintermediate and outer shells to form therewith a resonance chamber,Said inner Shell having an opening therein through which sound Waves maypass into the Space between said inner and intermediate shells, alongitudinally extending channel formed in a portion of Saidintermediate Shell, and a sleeve extending around a porton of thechanneled part of Said intermediate Shell to close portions of the outeropen faces of Said Channels to form bottle necks communicating with saidresonance chamber.

12. In a muliler, the combination of a Shell forming a passage for gasesthrough a muliler, a second Shell arranged about said i St Shell, anouter Shell arronged about both of said shells and forming with saidSecond Shell a resonator chamsaid first Shell having an opening throughWinch Sound Waves may pass into the space between Said first and secondnells, an end of Said second Shell having a longitudinally extendlngchannel formed therein, a sleeve arranged about portions of said firstShell and the channeled end of said second Shell, Said channeled portionforming With said inner Shell a passage of lesser cross section thespace between said first and second shells and forming with Said sleevea continuing passage between Said second Shell and said sleeve.

13. lin a mufer, the combination of a Shell forming a passage for gasesthrough a muftler, a Second Shell arranged about said first Shell, anouter Shell arranged about both of said Shells and forming With saidSecond Shell a resonator Chamber, said first Shell having an openingthrough which sound waves may pass into the Space between said first andsecond shells, an end of said Second Shell having a longitudinallyextending channel formed therein, the bottoms of said Channels engagingsaid first Shell, a sleeve arranged about part of the channelled portionof Said Second Shell, Said channelled portion forming with said firstShell a restricted passage for sound Waves which oonnects with arestricted passage formed by said channelled portion and said sleeve,Said latter restricted passage terminating in Said resonance Chamber,

14. In a mufier, the combination of a Shell forming a passage for gasesthrough a muliler, a second Shell arranged about said first Shell, anouter Shell arranged about both of said Shells, a head connecting saidouter Shell with said first Shell, said Second Shell terminatlng at adistance from Said head, said first Shell having an opening throughwhich sound Waves may pass from the interior thereof into the spacebetween Said first and second Shells, the end of Said second Shelladjacent to said head being provided with a longitudinally extendingchannel, and a sleeve secured to said head and extending about saidchannelled end of said Second Shell, whereby a v restricted passage isformed between Said first and Second Shells and which connects With apassage formed between said sleeve and said second Shell and terminatingin the Space between Said outer and second shells.

15. In a mufler, the combination of a Shell forming a passage for gasesthrough a mufiler, a second Shell arranged about Said first Shell, anouter Shell arranged about both of said Shells, a head connectng Saidouter Shell with Said first Shell, Said second Shell terminating at adistance from said head, Said first Shell having an opening throughwhich sound waves may pass from the interior thereof into the Spacebetween said first and Second shells, and an imperforate portionadjacent to Said head, and a sleeve secured to Said head and extendingabout the end portion of said Second Shell, wher-eby a restrictedpassage is formed between Said imperforate portion of said first Shelland the end portion of Said Second Shell, which passage connects With apas- Sage formed between Said sleeve and Said Second Shell andterminating in a space exterior to Said second Shell.

ROY J. MACKENZIE. LUCIEN L. I-IAAS.

